Overshoot current phase/amplitude control for hard disk drive write current

ABSTRACT

Devices and methods for generating a magnetic head-specific overshoot current which is combined with an alternating current waveform into a write current used by the magnetic head to store information on a magnetic medium. A processor analyzes the frequency of incoming write data and retrieves from a data table of an overshoot current amplitude and an overshoot current phase. This amplitude and phase information is sent to an overshoot current generator to generate an overshoot current that is responsive to the dynamic impedance properties of a magnetic write head during operation. The data table may have information related to one or many write heads, and the data table may be further subdivided based on additional dynamic characteristics of a write head that may affect the impedance thereof.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to control systems forhard disk drives, and, more specifically, the present invention providesa circuit for determining and applying an overshoot current (I_(os))with a selected amplitude and timing (phase) to a generated square wavecurrent (I_(sq)), which in combination is provided as a write current(I_(w)=I_(sq)+I_(os)) to a write head in a hard disk drive.

[0003] 2. Description of the Background

[0004] In a conventional hard disk drive, one or more magnetic media(disks) are written to and read from by magnetic heads. Typically, towrite a certain bit of information to a location on the magnetic medium,a write head is moved over the specified location on the hard disk,while a magnetic field is generated via coils in the magnetic head. Awrite current is then applied to coils in the write head, causing themagnetic field to be circulated through the hard disk medium, therebystoring information. By rapidly rotating the magnetic media mounted on aspindle, and further by rotating an arm of a gimbal with the magnetichead suspended on the end thereof radially across the surface of themedium, the magnetic head can write a large amount of information in ashort amount of time.

[0005] To enable the write head to determine when to generate a magneticfield to write information to the magnetic medium, a write current I_(w)is supplied to the write head. This write current I_(w) is generally aseries of current pulses (pulse train) that arrive at the write head atthe moment when the head travels over a location on the magnetic mediumto be written to. To enable faster writing, the frequency of the pulsetrain that makes up the write current I_(w) needs to be increased.However, as the frequency of the pulses increases, the leading edge ofthe pulse becomes distorted because “real world” electronics are notable to generate a perfect incoming square wave pulse, and furtherbecause the impedance of the write head will deform the pulse (asdescribed more fully below).

[0006] To at least partially correct these pulse deformation problems,and to allow for a higher frequency write current I_(w), an overshootcurrent I_(os) is typically added to the generated square wave I_(sq),the combination of the two currents becoming the write current(I_(w)=I_(sq)+I_(os)). The overshoot current allows the write pulses tohave a decreased (i.e., faster) rise time so that a higher frequencywrite current can be used to write information with a write head,thereby increasing the speed at which information can be recorded to themagnetic medium.

[0007]FIG. 10 generally shows this combination of currents. In FIG.10(A), a square wave current I_(sq) is shown as an imperfect square wavegenerated by a square wave generator. The rising edge of the square wavecurrent is not a perfect vertical line, and the response of the writehead to receiving this signal I_(sq) as the intended write current wouldnot be as intended by the system. FIG. 10(B), therefore, shows anovershoot current I_(os) with a given amplitude (Amplitude_(os)) that isgenerated to correct the deformities in the square wave current I_(sq).FIG. 10(B) shows that the square wave current I_(sq) is combined withthe overshoot current I_(os) after some time delay (Timing_(os)). Inother words, the overshoot current is generated, a small time delay(Timing_(os)) is waited, and the square wave current is then combined(via an adder) with the existing overshoot current I_(os). The combinedwrite current (I_(w)=I_(sq)+I_(os)) is shown in FIG. 10(C) as the resultof this addition. The resulting write current includes a faster risetime and will cause the write head to perform more closely to thecalculated intentions of the system. The amplitude (Amplitude_(os)) andthe timing or phase (Timing_(os)) of applying the overshoot current areboth predetermined and fixed in current systems.

[0008] The main problem with this conventional overshoot addition isthat the write pulses do not occur at the same frequency, and that thewrite head will respond differently (e.g., has a different impedance) atthese different frequencies. This aspect is depicted in FIG. 4. FIG. 4shows an exemplary write current waveform showing one complete writecurrent pulse and the front half of a second write current pulse. Asseen in the drawing, the initial write current pulse (square wave) has awrite frequency of f1 (wherein the period of the pulse itself is onlyhalf of this value, or 1/(2f₁)) . An overshoot current has been added tothe square wave current to correct for the distortion caused by theimpedance of the write head. The time delay between the initial currentpulse and next current pulse has a frequency of f₂ (period of 1/(2f₂)),and the next write current pulse has yet another frequency f₃ (period of1/(2f₃)). Therefore, each pulse (and time period between pulse) may havea separate frequency. The overshoot current amplitude and timing (phase)is not conventionally adjusted to account for these differentfrequencies.

[0009] The multiple frequency problem occurs because the write head hasa different impedance at different write data frequencies, and thisimpedance difference will distort the incoming write data current indifferent ways (see generally, FIG. 5). Therefore, a single overshootcurrent of a fixed amplitude and a fixed timing will not properlycorrect the distortion in the square waveform current at all possibleoperating frequencies. Instead, the applied overshoot current amplitudeand timing of application should be altered with each incoming writecurrent pulse to maximize the chance that the write head will correctlystore information in the magnetic medium. Solutions in this vein aredesired.

SUMMARY OF THE INVENTION

[0010] In at least one preferred embodiment of the present invention, adevice and method are provided for adjusting the amplitude and timing ofan overshoot current I_(os) that is combined with a generated squarewave current I_(sq) (or current “pulse”) to produce a write currentI_(w) in a write head for a magnetic recording medium. Because theimpedance of the write head changes at different writing frequencies,the write current waveform should be adjusted in a way that takes theseimpedance differences into account. Changing the offshoot currentamplitude and timing characteristics is one way to accomplish thisresult.

[0011] A hard disk drive according to the present invention preferablyanalyzes the incoming write data (data to be written to the magneticmedium) and uses a processor to continuously calculate the frequency ofthis incoming write data. This obtained frequency information is thenused by the processor to access a stored data reference table thatcorrelates each potential write data frequency to an overshoot currentamplitude and timing for each head in a hard disk drive. The referencetable may be stored in a memory such as a RAM (Random Access Memory) ora ROM (Read Only Memory) , in an administration section of the hard diskdrive medium, in a series of data latches or registers, or in any otherstorage medium.

[0012] The reference table may include data for just one single writehead or for a plurality of different heads. If data is stored for aplurality of different heads, these heads may represent all of the writeheads used with the particular magnetic mediums installed in the presenthard disk, or they may represent all of the heads with a certainproperty or characteristic. With the latter scenario, the same datareference table could be installed in a wide variety of hard disk drivesusing a wide variety of write heads, even though each particular diskdrive would only use a portion of the total reference table. Such asystem may reduce fabrication costs for the manufacture of the referencetable.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For the present invention to be clearly understood and readilypracticed, the present invention will be described in conjunction withthe following figures, wherein like reference characters designate thesame or similar elements, which figures are incorporated into andconstitute a part of the specification, wherein:

[0014]FIG. 1 shows a perspective view of a hard disk drive system;

[0015]FIG. 2 details an exemplary head-gimbal assembly for use with thepresent invention;

[0016]FIG. 3 shows a system block diagram of a conventional hard diskdrive;

[0017]FIG. 4 shows a write current waveform used by a write head tostore information on a magnetic disk medium;

[0018]FIG. 5 shows the relationship between various impedance propertiesof a write head versus operational frequency;

[0019]FIG. 6 depicts a low frequency current waveform 6(A), ideal 6(B)and actual 6(C) high frequency current waveforms, and the correspondingfrequency bandwidths 6(D);

[0020]FIG. 7 shows a conventional architecture for an R/W Channel IC andan R/W IC 7(A) and an R/W Channel IC and an R/W IC according to thepresent invention 7(B);

[0021]FIG. 8 shows a system block diagram of a hard disk drive accordingto the present invention;

[0022]FIG. 9 shows exemplary reference tables that hold one 9(A) ormultiple 9(B) relationships between a write data frequency and overshootcurrent amplitude and timing information or other write headcharacteristics 9(C); and

[0023]FIG. 10 shows exemplary current waveforms in a hard disk driveincluding a square wave current I_(sq) 10(A), an overshoot currentI_(os) 10 (B) , and a combined write current I_(w) 10(C).

DETAILED DESCRIPTION OF THE INVENTION

[0024] It is to be understood that the figures and descriptions of thepresent invention have been simplified to illustrate elements that arerelevant for a clear understanding of the present invention, whileeliminating, for purposes of clarity, other elements that may be wellknown. Those of ordinary skill in the art will recognize that otherelements are desirable and/or required in order to implement the presentinvention. However, because such elements are well known in the art, andbecause they do not facilitate a better understanding of the presentinvention, a discussion of such elements is not provided herein. Thedetailed description will be provided hereinbelow with reference to theattached drawings.

[0025]FIG. 3 generally indicates a system block diagram for aconventional hard disk drive. Two way communication to and from the harddisk drive occurs from a host computer, generally via some type ofcomputer bus such as an IDE, EIDE or SCSI bus. The information sent toand received from the host computer is received by the disk datacontroller, which may use a buffer RAM to facilitate communication oflarge amounts of data.

[0026] The disk data controller is connected to a Read/Write ChannelCircuit (“R/W Channel IC”), a Read/Write Circuit (“R/W IC”), a disksignal controller, and a microcomputer (sometimes referred to herein asa “processor”) capable of performing various calculations and operationson the data to be written to and read from the magnetic disk medium.Generally speaking, the disk data controller and the disk signalcontroller work with the R/W Channel IC, the R/W IC, and themicrocomputer to generate all of the signals used to write informationto or read information from the hard disk. These signals include thewrite current signals sent to the write head to write data to the harddisk, as well as the control signals that rotate the hard disk mountedon a spindle and move the magnetic head radially across the surface ofthe hard disk by rotating the arm on which the magnetic head is mounted.The microcomputer may be connected to one or more RAMs (Random AccessMemory) and/or ROMs (Read Only Memory) to facilitate the variouscalculations that are necessary to write data to and read data from amagnetic medium.

[0027] In order to rotate or spin the magnetic media that are mounted ona spindle, the microcomputer is connected to a spindle motor driver anda spindle motor. By controlling the spin of this spindle, themicrocomputer controls the speed at which the magnetic head flies overthe magnetic disk, and hence, the speed at which information can bewritten to the disk. There is also a SERVO driver and a voice coilactuator connected to the processor. The SERVO driver and the voice coilactuator provide the rotational movement of the arm of the hard diskthat includes the magnetic head attached thereto. This arm allows forradial movement of the magnetic head over the surface of the magneticmedium.

[0028] Data to be written to the magnetic medium is received from thehost computer and is transferred to the R/W Channel IC. The write datais then sent from the R/W Channel IC to the R/W Circuit where it isconverted into a write current that is sent to the write head to storeinformation on the magnetic medium. More specifically, the R/W ChannelIC feeds this write data to a square wave (or other alternating waveprofile) current generator in the R/W IC, which generates a square wavecurrent at a frequency determined by the write data received from theR/W Channel IC.

[0029] The R/W IC also includes an overshoot current generator which issynchronized to the square wave current generators. The generated squarewave current I_(sq) is then combined (via an adder circuit) with agenerated overshoot current I_(os) which, when combined, becomes thewrite current I_(w) that is sent to the write head to be used to writedata to the magnetic disk medium. In this conventional embodiment, theovershoot current amplitude and the timing for applying the overshootcurrent is predetermined and is not based on the frequency of theincoming write data. Because the characteristics of the write headchange as the write data frequency changes (as described more fullybelow), this inability to change is not preferred.

[0030] As generally described above, the write current I_(w) for a harddisk drive magnetic head is ideally a square wave current that can beproduced from a square wave generator within the hard disk drivecircuitry. FIG. 5 shows a relationship between the impedance propertiesof an exemplary write head versus the frequency of the write dataapplied to the write head. As shown in FIG. 5, the resistance of a writehead at high frequencies increases, and the inductance of the write headdecreases at high frequencies. Therefore, at high operationalfrequencies, the impedance properties of the write head will distort thewrite current waveform such that the current is no longer ideal tofacilitate writing to the hard disk medium. Thus, the write head isconsidered to have a narrow write frequency band because high frequencywrite currents I_(w) may not be effectively used. This problem becomeseven more pronounced when it is considered that each write head willperform differently (have different impedance values) at highfrequencies. Therefore, correcting for the write current distortions ishindered.

[0031] As a partial solution to minimize the write current distortionscaused by the write head impedance, the square wave current I_(sq)generated from a square wave generator is combined with on overshootcurrent I_(os) to create the actual write head current I_(w), accordingto:

I _(w) =I _(sq) +I _(os)

[0032] This overshoot current I_(os) compensates for the distortion ofthe square wave I_(sq) current by decreasing the rise time andincreasing the amplitude of the initial portion of the square wavecurrent pulse (as described in more detail above).

[0033] In conventional applications, however, this overshoot currentI_(os) is generated by an overshoot generator at a fixed amplitude andthe timing (phase) . So timing in which this overshoot current I_(os) isapplied to the square wave current I_(sq) is also fixed. The combinationis based only on the synchronization between the square wave generatorand the overshoot current generator. Because the write head hasdifferent impedance characteristics at different operationalfrequencies, the distortion of the square wave I_(sq) will vary atdifferent write current frequencies. Therefore, the overshoot currentI_(os) application at fixed times and at fixed amplitudes will notproperly correct the high frequency distortion problem for all cases.Additionally, as different write heads are used, each with its ownunique high frequency impedance characteristics, again the fixedovershoot current will not properly correct the distortion.

[0034]FIG. 6 further exemplifies the high frequency distortions of writecurrents I_(w) in write heads for magnetic media. At low frequencies(shown in FIG. 6(A)), the write current resembles a square wave with anadded offset (in this embodiment, “offset” means overshoot) intended todecrease the rise time of the non-ideal square wave. As write currentsof higher frequencies are presented to the write head, the impedanceproperties of the write head at high frequencies distort the writecurrent. Ideally (FIG. 6(B)), at high frequencies, the write currentwill resemble the low frequency write current waveform, except with ashorter pulse width. The added overshoot current will enable a quickresponse time. However, in actual current write heads (FIG. 6(C)), thehigh frequency impedance properties of the write head distort thecurrent waveform such that the rise time is increased to an unfavorableamount.

[0035]FIG. 6 also shows the result of these high frequency distortions.FIG. , 6(D) shows the resultant write current amplitude across variouswrite data frequencies (i.e., write current frequency band). The dottedline represents the actual frequency response (from FIG. 6(C)) and thesolid line represents the more ideal response that is depicted in FIG.6(B). The impedance of the write head at high frequencies causes acontraction of the write current frequencies that may be used with thewrite head. Under ideal conditions, the write current frequency bandwould be expanded to that shown in the solid line in FIG. 6(D).

[0036]FIG. 7 details exemplary models of the write current generatingcircuitry in the R/W IC and its connection with the R/W Channel IC. FIG.7(A) shows a conventional R/W IC circuit and interconnection, and FIG.7(B) shows an exemplary R/W IC circuit and interconnection according toat least one preferred embodiment of the present invention.

[0037] As seen in FIG. 7(A), the conventional R/W IC receives write datainformation from the R/W Channel IC which describes data to be writtento hard disk medium via the magnetic write head. This write data is thentransformed by the R/W IC into a write current I_(w) that is provided tothe write head. A square wave current generator then creates a pluralityof square wave current pulses that correspond to the write datainformation received from the R/W Channel IC. The generated square wavecurrent represents the “ideal” information to be written to the magnetichard disk medium.

[0038] Because of the high frequency impedance characteristics of thewrite head which will deform this ideal square wave, the R/W IC alsoincludes an overshoot current generator that generates an overshootcurrent I_(os) that is added to the generated square wave current I_(sq)to produce a combined write current I_(w) which is provided to the writehead. In the conventional hard disk drive circuit shown in FIG. 7(A),this overshoot current is set at a predetermined amplitude andpredetermined timing (phase) such that the overshoot current is alwayscreated in the same way. The square wave current generator and theovershoot current generator are fabricated in a Read Write IC. Thesquare wave current generator and the overshoot generator aresynchronized such that the overshoot current will get added to thegenerated square current according to a predetermined delay time.Specifically, the R/W IC is connected to the external clock and theoutput of the R/W Channel IC in such a way that the timing of the outputof the overshoot current and then the square wave current (after a shortdelay time) is synchronized by this external clock. In essence,regardless of the frequency of the generated square wave or theimpedance of the write head, the same overshoot current with the sameamplitude and phase will be used. Because the impedance of the writehead changes at different operating frequencies, and further becausedifferent write heads have different impedance characteristics, thiscircuit is not ideal to enable proper writing of information to themagnetic medium.

[0039]FIG. 7(B) shows one exemplary embodiment of an R/W-IC andinterconnection according to the present invention. The square wavecurrent generator again receives the write data information from the R/WChannel IC to produce square wave current pulses that correspond to thiswrite data to be written to the write head. However, rather thanapplying a predetermined amplitude/timing overshoot current to thisgenerated square wave current, the present invention preferablyprocesses the received write data and generates an overshoot currentthat matches the operating characteristics (e.g., impedance) of thewrite head at the current operating frequency (based on the analyzedwrite data frequency).

[0040] More specifically as shown in FIG. 7(B), the R/W Channel IC isalso connected to a processor which receives the write data and analyzesthe data to determine the frequency of the write data. This frequencychanges as different data is to be written to the hard disk drive, andthe processor preferably continuously analyzes the incoming write datato determine the write data frequency at that particular time.

[0041] The processor is also communicatively connected to a memory,which may be a RAM or ROM, an administration portion of the hard diskmedium, a register or latch, or any other type of electronic storagemedium. This storage medium preferably includes a data reference tablethat stores a relationship between various different write datafrequencies and the amplitude and timing (phase) of an overshoot currentthat should be added to a square wave current pulse to most effectivelywrite data to a magnetic medium using the write head. In other words,rather than adding a predetermined and unchanging overshoot current tothe generated square wave current pulse, the present invention is ableto analyze a local frequency of the write data and add a specificovershoot to the write data that compensates for the change in impedanceof the write head at different write data frequencies.

[0042] Returning to FIG. 7(B), after the processor calculates thecurrent write data frequency and retrieves the corresponding overshoottiming and amplitude values from the overshoot data reference table,this overshoot amplitude and timing information is preferably sent tothe overshoot current generator which thereafter generates an overshootcurrent with the selected characteristics. In the same way as in FIG.7(A), the overshoot current I_(os) is combined with the square wavecurrent I_(sq) to create the write current I_(w) that is sent to thewrite head (represented by the load in FIG. 7). By this analysis andselection method, the R/W IC of the present invention is able to providea more accurate write data waveform to the write head of a hard diskdrive, and to enable more accurate writing of information to a magneticmedium.

[0043] The use of this general algorithm creates desirable write currentproperties with a wider write frequency band for a write head than theconventional hard disk drive devices. This favorable response isindependent of head impedance changes due to write data frequencychanges. This method is also useful for different write heads withdifferent impedance characteristics. This method may also be independentof an impedance change that occurs due to write head heating duringoperation or any other characteristic of the write head that may changethe write head inductance as long as this changing characteristic ismade part of the reference data table as described more fully below.

[0044]FIG. 9 shows three exemplary embodiments of an overshoot referencedata table for use with the present invention. This table preferablyprovides a relationship between the frequency of the write data receivedby the R/W IC and the amplitude and timing of the an overshoot currentwaveform that should be added to a square wave current I_(sq) to producethe write current I_(w). Generally speaking, these values are labeled“Amplitude_(os)” and “Timing_(os)” in FIG. 10. FIG. 9(A) shows areference table in which each write data frequency corresponds to asingle delay timing (in picoseconds) and a single overshoot amplitude(in milliamps). FIG. 9(B) shows this table adapted so that eachfrequency of write data is associated with a specific timing andamplitude for a plurality of different write heads (Head A, Head B,etc.). FIG. 9(C) shows alternative write head characteristics that maybe made a part of the reference data table.

[0045]FIG. 9(A) shows the simplest form of the reference data table. Foreach of the write data frequencies (e.g., 50 MHz, 100 MHz, 150 MHz)there is a corresponding timing and a corresponding amplitude. Theovershoot waveform is generally a pulse, wherein the amplituderepresents the intensity of that pulse in milliamps. The overshoot isalso combined with the generated square wave at a certain time delaywhich is represented as the timing in picoseconds. The values for thetiming increase as the write data frequency increases. In thisembodiment, these values means ahead of time in which the overshootcurrent should be combined to square wave current. Therefore, thesevalues have negative.

[0046] As seen in FIG. 9(A), the values for the amplitude and the timinggenerally increase as the write data frequency increases, but anyrelationship may be employed using this table. Additionally, theselected write data frequency values are exemplary only, and variousvalues could be stored in the reference data table depending on thespecific write head employed or other factors.

[0047]FIG. 9(B) shows an expansion of the table in FIG. 9(A). In thereference data table of FIG. 9(B), there are two separate tables, onecorresponding to the timing of the overshoot current and onecorresponding to the amplitude of the overshoot current. For eachincoming write data frequency determined by the processor, there are aplurality of different timing and amplitude values labeled Head A, HeadB, etc. These different head values correspond to different write headsthat have different operating characteristics (e.g., different impedancevalues). For example, these different heads could correspond todifferent write heads that exist in the same hard disk. In this way,depending on which write head is currently being used for a writeoperation, the processor could locate the appropriate head in thereference data tables and determine the timing and amplitude for thathead at the calculated operating frequency.

[0048] Alternatively, these multiple heads may just represent all of thepossible write heads that may be used in a certain hard disk drive, orin a plurality of hard disk drives, for example that share a certaincharacteristic. A ROM that holds the data table could then be used in avariety of different hard disks with a variety of different write heads.Even though every line in the table may not be used in each manufacturedhard disk drive, the fabrication of the ROM holding the data table wouldbe less expensive because the same table could be repeatedly fabricated.In this way, the reference data table could be mass produced andflexible.

[0049]FIG. 9(C) shows an exemplary reference data table that includesadditional characteristics used to determine the overshoot currentamplitude and phase. For example, because of write head heating duringoperation or some other reason, the inductance of the write may changebased on more than just the frequency of the write data. Therefore, thereference data table of FIG. 9(C) shows that two characteristics, thefrequency of the write data and a measured inductance of the write headdue to other factors, are both used to select an overshoot currentamplitude and overshoot current timing. This table is exemplary and anycombination of inductance-altering factors may be used.

[0050] Looking now at FIG. 8, a high level system block diagram of ahard disk drive according to at least one presently preferred embodimentof the invention is shown. In most respects, this system block diagramis the same as that shown in FIG. 3 and described above. As in thatcase, two way communication with a host computer is facilitated througha disk data controller and a buffer RAM. Thereafter, the disk datacontroller, the disk signal controller, the R/W Channel IC, the R/W IC,and a microcomputer work together to provide the physical movement andlogical signals needed to read and write data from and to the hard diskmedium.

[0051]FIG. 8 also shows two new communications lines 50, 52 shown inbold in the diagram. These lines allow communication from the R/WChannel IC to the microcomputer (processor) 50 and from themicrocomputer to the R/W IC 52. As described more completely above, thefirst of these two new communications lines 50 allows for themicrocomputer to receive the write data information that is sent fromthe R/W Channel IC to the R/W IC. The microcomputer then analyzes thiswrite data to determine its frequency. The microcomputer may thenreference a data table in an associated memory device (RAM or ROM) orfrom an administration section of the hard disk medium itself, toretrieve an appropriate overshoot current amplitude and timing for thedetected write data frequency. Once retrieved from the reference table,this overshoot current amplitude and timing (phase) information are sentover the second of the new communication lines 52 from the microcomputerto the R/W IC.

[0052] Specifically, the overshoot information is sent to an overshootcurrent generator circuit so that the overshoot generator may create anovershoot current that is specifically designed for the write headoperating characteristics at the write data frequency. Within the R/WIC, a generated square wave current I_(sq) and the generated overshootcurrent I_(os) are then combined into a write current I_(w) that is sentout to the write head to enable the write head to record information onthe magnetic recording medium. In this way, a more accurate writecurrent may be sent to the write head so that the write head can moreaccurately record information in the hard disk drive.

[0053] The present invention may be incorporated into a variety ofdifferent hard disk drives in a variety of different ways. For example,FIG. 1 shows one presently preferred embodiment of hard disk driveincorporating the present invention therein. FIG. 1 generally shows thehead-disk assembly 10 and the R/W control circuit 11. The R/W controlcircuit 11 provides the interface between the hard disk drive and therest of the computer system, and provides the signal processing andcontrol functionality to the hard disk drive.

[0054] The R/W control circuit 11 includes an interface 24 whichconnects (typically by cable) to the bus of the computer system. Thisinterface 24 is connected to the hard disk drive controller 23 (HDDcontroller) and a signal processing LSI 22 (Large Scale Integratedcircuit). Together, the HDD controller 23 and the signal processing LSI22 provide the logical interface between the computer system and thestored contents of the hard disk. These component process data that isto be written to or read from the hard disk, and they control thevarious hard disk drive components (e.g., the voice coil motor 17, thearm 18, and the spinning of the medium 13) to enable the reading fromand writing to the hard disk drive.

[0055] The head-disk assembly 10 is connected to the R/W control circuit11 via matching interfaces 25-2 and 25-1. The signal from the R/Wcontrol circuit 11 is sent to the FPC 16. The head-disk assembly 10includes a carriage 15 and a plurality of arms 18 that hold a suspension19 with a magnetic head 14 at the end of the suspension and arm. Thehead-disk assembly 10 also includes a spindle 12 and a plurality ofmagnetic disks 13 (five shown) wherein the spindle rotates the magneticdisks at a high speed so that the magnetic head 14 travels across thedisk. As the magnetic disk 13 spins, the carriage 15 rotates the arm 18(via the voice coil motor 17) which moves the magnetic head 14 in aradial direction across the magnetic medium 13. Coupled with therotation of the magnetic medium 13, this radial motion allows themagnetic head to travel across all areas of the disk 13 to read andwrite information on the disk. Each disk 13 preferably includes its ownarm/head combination, and each disk may include a plurality of arm/headcombinations (one on each side) if the disk is capable of storinginformation on both sides.

[0056]FIG. 1 also shows the R/W IC 20 as used in the present inventionto add a dynamically determined overshoot current to a generated squarewave current to more accurately control the writing of information tothe hard disk 13 via the magnetic head 14. The R/W IC 20 receives writedata information from the R/W Channel IC and receives overshootamplitude and timing information from a processor on the R/W controlcircuit 11. The R/W IC 20 is then connected, via a plurality oftransmission lines 21 to each of the magnetic heads 14 used to writeinformation to the various surfaces of the plurality of hard diskmediums 13. Each transmission line 21 preferably runs along the edge ofeach arm 18, across the suspension area 19 and into the magnetic head14, where the combined square wave plus overshoot signal is used towrite information to the hard disk medium 13.

[0057] More specifically, FIG. 2 shows an exemplary hard disk drivehead-gimbal assembly with the present R/W IC installed thereon. FIG. 2includes the arm 18, suspension 19, and magnetic head 14 of aconventional hard disk drive gimbal. Generally, the arm 18 rotates abouta shaft (carriage) that allows the magnetic head 14 to move in a radialdirection over a hard disk medium. As the medium rotates about it axis(spindle), the magnetic head 14 is therefore able to reach all areas ofthe magnetic medium to read and write data thereto.

[0058] According to the present invention, the R/W IC may be installedon the side of the arm 18, such that it is part of the head-gimbalassembly. The R/W IC preferably receives both the write data from theR/W Channel IC and the overshoot amplitude and timing information fromthe processor. The R/W IC includes the overshoot current generator, thesquare wave current generator, and a circuit to combine these twowaveforms into the write data current I_(w). This write data currentI_(w) is then sent through transmission line 21 a to the suspension 19and through transmission line 21 b to the write head 14. The write head14 then applies the write current to the magnetic medium to write datato the medium as described above.

[0059] There are many other orientations of the present invention thatwill be readily apparent to those skilled in the art, and those examplesspecifically mentioned should not be used to limit the inventionthereto. For example, the R/W IC could be located in the R/W controlcircuit 11 board, and the write current I_(w) could be transmitted tothe write head by a longer transmission line. Additionally, the R/WChannel IC could be mounted on the suspension. In this case, thetransmission line will be shorter. Also, the reference data table may bestored in a storage medium that is a part of the head-gimbal assembly,or at any other location in the hard disk drive.

[0060] Finally, it has been supposed through this disclosure that theideal current waveform to be provided to the write head is a train ofsquare wave pulses. However, other alternating (repetitive) waveformscould also be used, and different write heads may be designed to performmore accurately or faster with various different write currentwaveforms. The present invention may be adapted to any alternating orrepeating waveform in that is adds a corrective current (e.g., theoffshoot current) to the generated “ideal” current to alleviate theloading effects of the changing write head impedance.

[0061] Nothing in the above description is meant to limit the presentinvention to any specific materials, geometry, or orientation of parts.Many part/orientation substitutions are contemplated within the scope ofthe present invention. The embodiments described herein were presentedby way of example only and should not be used to limit the scope of theinvention.

[0062] Further, additional embodiments may take on a form as follows. Amagnetic recording apparatus, comprising a magnetic recording medium; amagnetic head for applying a recording field to the magnetic medium; anda circuit for supplying alternating current to raise said recordingfield, wherein said circuit includes means for adding an overshootcurrent to the alternating current, and means for controlling the timingof adding said overshoot current to said alternating current.

[0063] A magnetic recording apparatus according to the above paragraph,further comprising: a data table which includes a relationship between afrequency of said alternating current and a phase and an amplitude ofthe overshoot current.

[0064] A magnetic recording apparatus according to the above paragraph,wherein said data table is recorded in a specific area of said magneticrecording medium.

[0065] A magnetic recording apparatus according to the above paragraph,further comprising: a non-volatile memory to store said data table.

[0066] A magnetic recording apparatus according to the above paragraph,further comprising: a register or a memory in which said table isloaded.

[0067] A magnetic recording apparatus according to the above paragraph,wherein a relationship between a load impedance of said magnetic headand a phase and amplitude of an overshoot current is recorded in saiddata table.

[0068] A magnetic recording apparatus, comprising: a plurality ofmagnetic recording media; a plurality of magnetic heads for applying arecording field to the magnetic recording medium; and a circuit forsupplying alternating current to raise said recording field of eachmagnetic head, wherein said circuit includes means for adding overshootcurrent to the alternating current, means for controlling the timing ofadding said overshoot current to said alternative current, wherein saidcircuit controls the timing of adding said overshoot current to saidalternative current.

[0069] A method of controlling a magnetic recording apparatus thatgenerates a recording current to be supplied to a magnetic head, byadding an overshoot current to an alternating current, comprising thesteps of: generating a recording current of a predetermined frequency;referring to a data table which describes a relationship between thefrequency of said alternating current and a phase and amplitude of anovershoot current; and adding said overshoot current to said alternatingcurrent.

[0070] Although the invention has been described in terms of particularembodiments in an application, one of ordinary skill in the art, inlight of the teachings; herein, can generate additional embodiments andmodifications without departing from the spirit of, or exceeding thescope of, the claimed invention. Accordingly, it is understood that thedrawings and the descriptions herein are proffered by way of exampleonly to facilitate comprehension of the invention and should not beconstrued to limit the scope thereof.

What is claimed is:
 1. A hard disk drive subcircuit for generating awrite head current to write information on a magnetic medium,comprising: an alternating current waveform generator; an overshootcurrent generator; and a processor, wherein said processor is adapted toanalyze incoming write data and output overshoot information to theovershoot current generator, and further wherein said overshoot currentgenerator is adapted to generate an overshoot current responsive to saidreceived overshoot information.
 2. A hard disk drive subcircuitaccording to claim 1, wherein said alternating current waveform is asquare wave current.
 3. A hard disk drive subcircuit according to claim1, further comprising: means for combining the generated alternatingcurrent with the generated overshoot current into a write head current.4. A hard disk drive subcircuit according to claim 3, wherein saidcombined write head current is transmitted to a write head to recordinformation on a magnetic storage medium.
 5. A hard disk drivesubcircuit according to claim 1, wherein said overshoot informationincludes an overshoot current amplitude and an overshoot current phase.6. A hard disk drive subcircuit according to claim 5, wherein saidprocessor analysis calculates the frequency of the received write data.7. A hard disk drive subcircuit according to claim 6, furthercomprising: a reference data table, wherein said reference data tableprovides a relationship between the write data and a correspondingovershoot current amplitude and overshoot current phase, wherein saidprocessor retrieves an overshoot amplitude and phase based on thedetermined frequency of the received write data that was analyzed.
 8. Ahard disk drive subcircuit according to claim 7, wherein said referencedata table is stored in a non-volatile memory.
 9. A hard disk drivesubcircuit according to claim 7, wherein said reference data table isstored in an administration portion of a magnetic hard disk drivemedium.
 10. A hard disk drive subcircuit according to claim 9, furthercomprising: a register or memory to which the reference data table isloaded for access by the processor.
 11. A hard disk drive subcircuitaccording to claim 7, wherein said reference data table includes aplurality of relationships between received write data and acorresponding overshoot current amplitude and overshoot current phase,wherein each of said plurality of relationships represents datacorresponding to a different write head.
 12. A hard disk drivesubcircuit according to claim 6, wherein said alternating currentgenerator generates a current waveform with a frequency corresponding tothe frequency of the received write data current as determined by theprocessor.
 13. A disk drive subcircuit according to claim 1, furthercomprising: a hard disk drive gimbal assembly including an arm with amagnetic write head attached at the end of the arm, wherein saidalternating current generator and said overshoot current generatorreside in a read/write integrated circuit that is attached to saidgimbal assembly, and wherein said read/write integrated circuit and saidmagnetic write head are connected by a transmission line.
 14. A diskdrive subcircuit according to claim 13, further including a magneticrecording medium disposed proximate to said magnetic write head suchthat said magnetic write head is adapted to record information on saidmagnetic medium via the provided write head current.
 15. A method forproviding a write data current to a write head, comprising the steps of:receiving write data information; analyzing said write data informationto determine the frequency of the write data; retrieving overshootinformation that corresponds to said determined frequency of thereceived write data from a data table; generating an alternating currentwave at said determined frequency; and adding an overshoot currentwaveform based on said retrieved overshoot information to said generatedalternating current wave to generate a write current.
 16. The method ofclaim 15, wherein said alternating current is a square wave current. 17.The method of claim 15 further comprising the step of: transmitting saidwrite current to a write head to record information on a magneticstorage medium.
 18. The method of claim 15, wherein said overshootinformation includes an overshoot current amplitude and an overshootcurrent timing delay.
 19. The method of claim 15, wherein said datatable resides in a memory of a hard disk drive.
 20. The method of claim15, wherein said data table resides in an administration portion of amagnetic storage medium.
 21. The method of claim 15, wherein said datatable stores the relationship between the write data frequency and theovershoot current amplitude and timing delay for a plurality ofdifferent write heads.